The present invention relates to a sine wave controller circuit for use with a neutral-point clamped inverter as disclosed in U.S. Pat. No. 5,120,986 to S. Shekhawat, which is hereby incorporated by reference. The reference patent discloses a sine wave synthesis controller circuit intended to be utilized in conjunction with a digitally-controlled neutral-point clamped inverter to produce a sinusoidal waveform from a direct voltage source. The circuit is configured so that it provides two separate control signals, +PWM and -PWM, to the logic controller of the neutral-point clamped inverter. The +PWM control signal relates to the regulation of the positive portion of the synthesized waveform, and the -PWM control signal relates to the regulation of the negative portion of the synthesized waveform. These control signals direct the production of a sinusoidal waveform in response to a reference sine wave, the instantaneous voltage output of the neutral-point clamped inverter, and positive and negative reference voltages.
One problem associated with such waveform production is instability of the synthesized waveform as a result of noise and logic malfunction. There may be instances when either noise in the circuit or a logic malfunction shoot through the circuit and cause the +PWM and -PWM signals to be generated coincidentally. This malfunction causes the semiconductor switches in the neutral-point clamped inverter to fire simultaneously producing instability in the waveform.